The Department of Education has instructed schools to cut the pay of up to 17,000 secretaries, caretakers, cleaners and other non-teacher staff.
These staff are employed by schools, not the Department, and their pay is funded through State grants.
Schools have been directed to impose pay cuts on a par with those applied to public servants in last year's budget.
The trade union IMPACT, which represents the workers, has said it will challenge the pay cut which it has described as thoughtless and ridiculously harsh.
It says many of those workers are currently earning barely above the minimum wage.
The cuts will be implemented from January.
Irish Primary Principals' Network spokesman Sean Cottrell responded said the cuts were ‘beyond belief’.
He said secretaries and caretakers play a pivotal in the functioning of schools and cutting their pay will mean hitting the lowest paid workers in education.